The development of the intestine and early establishment of commensal bacteria is important for rapid growth and enteric disease resistance of the modern broiler. Three studies measured the impact of yeast derivatives in diets of broilers. The objective of the first study was to determine if yeast products alone or in combination effected performance or gut morphology of broilers during a mild coccidia challenge. Day-old Cobb 500 chicks were placed in floor pens on litter seeded with coccidia and fed diets with or without yeast products. The objectives of the second and third studies were to 1) evaluate the effect of feeding cecal droppings collected from heavy (HW) or low weight (LW) broilers on performance and 2) to determine if dietary supplementation with yeast derivatives would effect growth and gut morphology in broilers fed the cecal droppings from HW or LW populations. Cobb 500 chicks were divided into two groups (HW or LW microflora; n=1400/group) and given access to the cecal droppings for a period of 48 hours then given 1 of 4 diets. The results from the studies showed that in a challenge setting, yeast products were not detrimental to growth. Inclusion of single yeast derivative or nucleotides was more beneficial than combination of these products for intestinal morphology. Cecal droppings from HW vs. LW birds did not have an effect on performance of birds. However, interactions of cecal dropping source and diet did affect intestinal morphology.